1. Field of the Invention
The present invention relates to a lens barrel including a cam ring and a rotational ring. The cam ring moves along an optical axis direction while rotating about the optical axis by rotation of the cam ring.
2. Description of the Related Art
A type of lens barrel including a cam ring and a rotational ring wherein the cam ring moves along an optical axis while rotating about the optical axis by rotation of the cam ring is well-known in the art. In this type of lens barrel, the rotational ring is positioned around the cam ring. This arrangement has been a cause of increasing the diameter of the lens barrel. However, it cannot be said that miniaturization of such a type of lens barrel has been extensively studied.
The present invention provides the aforementioned type of lens barrel which has structure making it possible to miniaturize the lens barrel, especially the diameter thereof.
For example, a lens barrel is provided, including a cam ring which is rotated about an optical axis to move at least one lens group in the optical axis direction via at least one cam groove formed on the cam ring, and a rotational ring which transfers a rotational motion to the cam ring. The rotational ring can include at least one rotation-transmission arm extending in the optical axis direction. The cam ring can include at least one engaging recess which is formed on an outer peripheral surface of the cam ring, and in which the rotation-transmission arm is slidably inserted to be relatively movable in the optical axis direction, and an outer flange formed on an outer peripheral surface of the cam ring to form a slot which penetrates therethrough in the optical axis direction between the outer flange and a bottom radial surface of the engaging recess so that the rotation-transmission arm is slidably inserted in the engaging recess through the slot.
It is desirable for the shape of the engaging recess to substantially correspond to the rotation-transmission arm, and wherein a radial depth of the engaging recess is substantially the same as a radial thickness of the rotation-transmission arm.
The cam ring is movable in the optical axis direction with respect to the rotational ring, the rotation-transmission arm and the engaging recess can be slidably engaged to be movable in the optical axis direction.
It is desirable for the rotational ring to be prevented from moving in the optical axis direction.
The lens barrel can further include a stationary barrel positioned around the cam ring and include at least one cam-ring guiding cam groove formed on an inner peripheral surface thereof, wherein the cam ring is rotated about the optical axis while moving in the optical axis direction in accordance with a profile of the cam-ring guiding cam groove.
It is desirable for the rotational ring to be positioned in the stationary barrel so as to be rotatable about the optical axis without moving in the optical axis direction with respect to the stationary barrel.
The lens barrel can further including a movable ring positioned around the cam ring, the movable ring being movable in the optical axis direction, and a plurality of first bayonet prongs being formed on the movable ring. The outer flange can include a plurality of second bayonet prongs which are engaged with the plurality of first bayonet prongs so that the cam ring and the movable ring move together in the optical axis direction.
It is desirable for the lens barrel to further include another movable ring positioned between the cam ring and the movable ring, wherein each of the movable ring and the another movable ring is guided linearly in the optical axis direction without rotating about the optical axis, and wherein the another movable ring projects forward from a front end of the movable ring when the lens barrel is in operation.
The lens barrel can include a motor which generates the rotational motion, so that the rotational ring transfers the rotational motion from the motor to the cam ring.
The lens group can include two movable lens groups, and the cam groove formed on the cam ring can includes a plurality of first cam grooves, formed on an inner peripheral surface of the cam ring, for moving one of the two lens groups in the optical direction in a predetermined moving manner, and a plurality of second cam grooves, formed on an outer peripheral surface of the cam ring, for moving the other of the two lens groups in the optical direction in a predetermined moving manner.
The lens barrel can be a zoom lens barrel having a zoom lens optical system including the lens group, a focal length of the zoom lens optical system varying by rotation of the cam ring.
The rotation-transmission arm and the engaging recess can include a plurality of rotation-transmission arms and a corresponding plurality of engaging recesses, respectively. The plurality of rotation-transmission arms are engaged in the corresponding plurality of engaging recesses from the rear end of the cam ring in the optical axis direction, respectively.
In another embodiment, a lens barrel is provided, including a rotational ring driven to rotate about an optical axis by a motor, a cam ring rotated about an optical axis by receiving a rotational motion of the rotational ring to move at least one lens group in the optical axis direction via at least one cam groove formed on the cam ring. The rotational ring can include a plurality of rotation-transmission arms extending in the optical axis direction. The cam ring can include a plurality of engaging recesses which are formed on an outer peripheral surface of the cam ring, and in which the plurality of rotation-transmission arms are slidably inserted to be relatively movable in the optical axis direction with respect to the plurality of engaging recesses, respectively, and an outer flange formed on an outer peripheral surface of the cam ring to form a plurality of slots which penetrate therethrough in the optical axis direction between the outer flange and bottom radial surfaces of the plurality of engaging recesses so that the plurality of rotation-transmission arms are inserted in the plurality of engaging recesses through the plurality of slots, respectively.
In another embodiment, a lens barrel is provided including a cam ring which is rotated about an optical axis to move at least one lens group in the optical axis direction via at least one cam groove formed on the cam ring, and a rotational ring which transfers a rotational motion to the cam ring. The rotational ring can include at least one rotation-transmission arm extending in the optical axis direction. The cam ring can includes at least one engaging recess which is formed on an outer peripheral surface of the cam ring, and in which the rotation-transmission arm is slidably inserted to be relatively movable in the optical axis direction, and an outer flange formed on an outer peripheral surface of the cam ring to bridge the engaging recess in a circumferential direction, so that the rotation-transmission arm is slidably inserted in the engaging recess so as to be positioned inside of the outer flange in a radial direction.
It is desirable for the rotation transmission arm to also extend in a circumferential direction of the rotational ring, and for the slots and the engaging recess to be also formed in the circumferential direction in accordance with the rotation transmission arm, the engaging recess extending in an area wherein the cam groove of the cam ring is not formed.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2001-335561 (filed on Oct. 31, 2001) which is expressly incorporated herein by reference in its entirety.